#include "ima_enc.h"
/* Intel ADPCM step variation table */

static int indexTable[16] = {
	-1, -1, -1, -1, 2, 4, 6, 8,
	-1, -1, -1, -1, 2, 4, 6, 8,
};

static int stepsizeTable[89] = {
	7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
	19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
	50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
	130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
	337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
	876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
	2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
	5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
	15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};




void decode(CodecState* state, u8* input, int numSamples, s16* output)

{

    u8 *inp;		/* Input buffer pointer */

    s16 *outp;		/* output buffer pointer */

    int sign;			/* Current adpcm sign bit */

    int delta;			/* Current adpcm output value */

    int step;			/* Stepsize */

    int valpred;		/* Predicted value */

    int vpdiff;			/* Current change to valpred */

    int index;			/* Current step change index */

    int inputbuffer;		/* place to keep next 4-bit value */

    int bufferstep;		/* toggle between inputbuffer/input */



    outp = output;

    inp = input;



    valpred = state->valprev;

    index = state->index;

    step = stepsizeTable[index];



    bufferstep = 0;

    

    for ( ; numSamples > 0 ; numSamples-- ) {

	

	/* Step 1 - get the delta value */

	if ( bufferstep ) {

	    delta = inputbuffer & 0xf;

	} else {

	    inputbuffer = *inp++;

	    delta = (inputbuffer >> 4) & 0xf;

	}

	bufferstep = !bufferstep;



	/* Step 2 - Find new index value (for later) */

	index += indexTable[delta];

	if ( index < 0 ) index = 0;

	if ( index > 88 ) index = 88;



	/* Step 3 - Separate sign and magnitude */

	sign = delta & 8;

	delta = delta & 7;



	/* Step 4 - Compute difference and new predicted value */

	/*

	** Computes 'vpdiff = (delta+0.5)*step/4', but see comment

	** in adpcm_coder.

	*/

	vpdiff = step >> 3;

	if ( delta & 4 ) vpdiff += step;

	if ( delta & 2 ) vpdiff += step>>1;

	if ( delta & 1 ) vpdiff += step>>2;



	if ( sign )

	  valpred -= vpdiff;

	else

	  valpred += vpdiff;



	/* Step 5 - clamp output value */

	if ( valpred > 32767 )

	  valpred = 32767;

	else if ( valpred < -32768 )

	  valpred = -32768;



	/* Step 6 - Update step value */

	step = stepsizeTable[index];



	/* Step 7 - Output value */

	*outp++ = valpred;

    }



    state->valprev = valpred;

    state->index = index;

}